C语言产生随机字符串

//产生长度为length的随机字符串  char* genRandomString(int length)  {      int flag, i;      char* string;      srand((unsigned) time(NULL ));      if ((string = (char*) myMalloc(length)) == NULL )      {          myLog("Malloc failed!flag:14\n");          return NULL ;      }        for (i = 0; i < length - 1; i++)      {          flag = rand() % 3;          switch (flag)          {              case 0:                  string[i] = 'A' + rand() % 26;                  break;              case 1:                  string[i] = 'a' + rand() % 26;                  break;              case 2:                  string[i] = '0' + rand() % 10;                  break;              default:                  string[i] = 'x';                  break;          }      }      string[length - 1] = '\0';      return string;  }